Generally, platinum wires are used; Pt100 is the acronym of themost common temperature resistance.

The accuracy is computed as follows:

A-class

+/-(0.15°C + 0.002*|T|), T in°C

B-class

+/-(0.3°C + 0.005*|T|), T in°C

These sensors are mandatory for highly accurate temperaturemeasurements. For all other needs, thermocouples are enough.

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Fluid flow

General concepts

Volume flow is defined as the volume ofgas/liquid that crosses a surface perpendicularto the velocity in the unit time. Measurementunit: m3/s in the S.I.

Q=[V]/[t] = [S].[v]; SI: {m3

/ s}

Mass flow is defined as the mass of gas/liquidthat crosses a surface perpendicular to thevelocity in the unit time. Measurement unit:Kg/s in the S.I.

G=[m]/[t] = [d].[S].[v]; SI: {Kg/s}

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Fluid flow measurement:

Venturi meter

The fluid flow gives rise to a pressure drop, which depends on theflow itself. The flow value is calculated from the pressure differencemeasurement: P2–

P2.

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Fluid flow measurement:

rotameter

The gas flows from the base inlet to theupper aperture of the rotameter.

The float is lifted upwards until the viscousdrag force is in equilibrium with gravity.

They are generally used with low flows, dueto high head losses.

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Fluid flow measurement:

thermal flow meter

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Fluid flow measurement:

thermal flow meter

There are two different configurations: inline and bypass.

In the inline configuration, the sensor is placed in a narrowingof the tube, resulting in high head losses.

In the bypass configuration, the sensor is placed in parallel tothe main flow: head losses are consequantly reduced.However, in this case the time-response is poorer.

In the inline configuration (see next slide), the gas is heated bythe resistor R1. The heat is convection-transported to thesensor R2. Depending on the gas flow, the temperature at R2will be different.

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Fluid flow principles: Bernoulli‘s theorem

Bernoulli’s equation:

z + P/gρ

+ v2

/ 2 g = constant

GravimetricPotentialEnergy

z = height

Pressure Energy

P = static pressure

ρ

= fluid density

Kinetic Energy

v = fluid velocity

The total mechanical energy of the flowing fluid,comprising the energy associated with fluid pressure,the gravitational potential energy of elevation, and thekinetic energy of fluid motion, remains constant.

Bernoulli's theorem is the principle of energyconservation for ideal fluids in steady, or streamline,flow.

g

is the gravityaccelarationconstant [L / t2]

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Bernoulli Theorem:

Example of application

z = constant

Compressed liquid in thepipe

Low pressure/high speedliquid at the shower outlet

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Fluid flow principles:

laminar/turbulent flow

Laminar flow: the fluid streamlines flows along parallel layers.

Turbulent flow: the fluid streamlines are wrapped in vortexes.

Turbulent flow

Laminar flow

Navier-Stokes equations

describe the motion of a fluid.

Navier-Stokes are non-linear partial differential equations, with nogeneral solution. Computational techinque must be used to solve thesystem.

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Fluid flow principles:

laminar/turbulent flow

Transition from laminar to turbulent flow is related by an adimensionalnumber: Reynolds number, Re.

In any case, a resin filter is generally used to lower the ion content of thecooling fluid.

Recently, FC stacks use glycol as a cooling medium. While givingcompatibility problems with polymeric materials inside the stack, thistechnology solves the corrosion problems which usually happen with metalheat exchangers.

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System integration issues:

cogeneration

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System integration issues:

cogeneration

The fuel cell stack is sized to meet the heatrequirements of the hot water user.

The excess electric power is sent to the grid.

The fuel cell water circuit is filled with demineralisedwater.

The filling of the boiler is regulated by the waterdemand of the final user.

The heat produced by the fuel cell is re-directed to a metal-hydride reservoir,which is heated via a heat exchanger.

Depending on the characteristics of thesystem, the power developed could belimited by the heat-transfer through themetal hydride bed.

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Pumps

What is a pump?

A pump is a device used to move liquids or slurries. Apump moves liquids from lower pressure to higherpressure, and overcomes this difference in pressure byadding energy to the system.

Gas pumps are generally referred as “compressors”.

Main pump categories:

Positive displacements pumps:

Kinetic.

Open Screw.

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Pumps

Reciprocating pumps:

Piston pumps.

Diaphragm pumps.

Rotary pumps:

Gear pumps.

Rotary vane pumps.

Screw pumps.

Fluid Ring.

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Compressors

What is a compressor?

A pump is a device used to move a gas from a lowpressure zone o an higher pressure zone: the deviceovercomes this difference in pressure by adding energy tothe system.

Main compressor categories:

Positive Displacement (axial, centrifugal).

Continuous flow compressors (rotary, reciprocating).

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Compressors

General principle:

Energy is transferred to the gas phase continuously from the lowpressure zone to the high pressure zone.

Two main types:

1.Centrifugal (axial and radial).

2.Peripherals (single stage, multiple stage).

Continuous-flow compressors are machines where the flow iscontinuous, unlike positive displacement machines where the flow isfluctuating. Continuous flow machines are also classified asturbomachines, and are generally smaller in size and produce lessvibration than their counterpart positive displacement units.

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Compressors

Centrifugal compressors:

The flow in a centrifugal compressor enters the impeller in an axialdirections and exits in a radial direction. In a typical centrifugalcompressor, the fluid is forced through the impeller by rapidly rotatingblades. The velocity of the fluid is converted to pressure, partially inthe impeller and partially in the stationary diffuser.

Typically centrifugal compressor are used in the process industry andin the aerospace applications in several kind of configurations: singleand multiple stages.

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Ejectors

Ejectors are the simplest among all types of pumps and compressors:

They do not have any moving part.

Ejectors are widely used in fuel cells system for anode recirculation.

Based on Bernoulli’s Principle:

Low pressure zone induced by thecontraction in B causes a fluid flow inA: this is a conseguence of theconservation of energy principle.

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Controls

Fundamentals of Control Systems.

SISO Control Systems.

PID Control Loops.

MIMO Control Systems.

Model Predictive Control Basics.

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Fundamentals of Control Systems

Measured Variables and Controlled Variables

A process consists of several measured and controlled variables.

A Control System is a device able to manage the behaviour of aprocess.

The simplest control system is called SISO:

Single Input–

Single Output

1 Measured Var

(Single Input)

1 Controlled Var

(Single Output)

Control

System

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SISO Systems

There are plenty of Single Input–

Single Output controlsystems.

SISO Systems Families:

On-Off Controls.

Proportional Controls.

PID.

On-Off and PID are the most common type of controllers.

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PID Controllers

Proportional Integrative and Derivative Controllers

Are quite common and widely used in process controlsystems.

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MIMO Control Systems

Multiple Input–

Multiple Output Control System

Measured Vars

Control

System

Controlled Vars

Complex Control Loops may require advanced logic in order the keep the process instable conditions.

Typical example are axial furnaces where multiple temperature probe should maintain agiven profile. Several power controller must be coordinated in a MIMO controller toreach the desired temperature profile.

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Model Predictive Control

MPCis an advanced method used in process controlwhere many variables must be controlled together in orderto reach a certain target.

MPC controller target is different from the “Set-Point” ofSISO and MIMO controllers: typically an MPC target couldbe toOPTIMIZE

a process in order to reduce costs of rawmaterials or energy.

MPC rely on dynamic models of the process, used topredict the behaviour of the dependent vs independentvariables.